In motors for critical drive applications, e.g. internal combustion engines or electric motors, it is often required that the operating state of the motor be outputted in the form of a signal, e.g.
“Drive system good” or “Drive system bad.”
This allows prompt repair or replacement of a defective motor.
This is especially applicable to fans in mobile radio installations, which must be regularly monitored as to whether they are rotating and, if so, whether their rotation speed lies above a predetermined limit that ensures cooling of the mobile radio installation.
It is known from DE 43 40 248 A1 and corresponding U.S. Pat. No. 5,845,045, JESKE, to modify the rotation speed of an electric motor, as a function of the temperature of a sensor, so that the motor runs quickly (e.g. at 4500 rpm) at high sensor temperatures and slowly (e.g. at 1500 rpm) at low temperatures. With this known motor, monitoring is moreover performed at regular intervals as to whether its rotation speed falls below a predetermined alarm rotation speed of, for example, 1000 rpm; and if such is the case, an alarm signal is generated.